What is the primary characteristic of a pressure compensated Thorpe Tube?

The primary characteristic of a pressure compensated Thorpe Tube is its ability to read accurately regardless of patient condition. This design integrates a unique mechanism that allows it to provide accurate flow readings even if there are variations in the downstream pressure as experienced during varying patient conditions or different delivery devices.

Essentially, the Thorpe Tube functions by allowing the gas flow to pass through a vertical tube, where the height of the float within the tube indicates the flow rate. In a pressure compensated design, this float is calibrated to adjust accordingly to maintain an accurate reading under different pressures. Therefore, even if a patient requires a higher flow or if there is some reduction in available pressure (for instance, due to an obstruction or the patient's breathing effort), the Thorpe Tube will still provide a reliable flow measurement.

In contrast, the other choices focus on limitations rather than the strength of the design. For instance, being dependent on patient flow would imply inconsistency, while inaccuracies under obstruction and operation without a constant pressure source both highlight situations where the Thorpe Tube might fail to provide reliable readings, which the pressure compensated version is specifically designed to avoid.